1. Field of the Invention
The present invention relates generally to scanning electron microscopes, and more particularly to a portable high resolution scanning electron microscope column using permanent magnet electron lenses.
2. Brief Description of the Prior Art
Prior art scanning electron microscopes are large and complicated structures, each system designed for a particular set of parameters. A scanning electron microscope has an electron gun for injecting high speed beams of electrons into one end of a column. Magnetic lenses in the column focus and sweep the beam, aimed at a specimen positioned in a chamber at the opposite end of the column. The electron gun, column and specimen chamber of the prior art are an integral assembly connected to a system of vacuum pumps and drive electronics. A major disadvantage of these prior art systems is their lack of flexibility. For example, if a specimen does not fit a particular SEM chamber, a different SEM with an appropriate specimen chamber must be found. In addition to the inflexibility of the specimen chamber, prior art SEM columns are also designed for particular applications. One design might be optimized for high resolution at low primary beam voltages, while another might be optimized for high primary voltages. Currently, different requirements of this kind demand the use of different scanning electron microscopes. A primary contributor to the lack of flexibility in SEM systems is the size and complexity of the SEM column. Columns contain magnetic electron lenses, with magnetic fields supplied by large high current density electromagnets. These large magnets contribute to the column internal volume, which along with the specimen chamber, must be evacuated to allow the passage of the high speed electrons. The large internal volume of these structures naturally requires a large, complicated vacuum system. Any attempt to reduce the size of the electromagnets results in high current losses in the magnet coils, which then require bulky, complicated cooling systems.
Electromagnets in early systems were a problem due to inadequately regulated power supplies which caused current variations and corresponding magnetic field variations. As a result of this, early attempts were made to design permanent magnet systems which were found to provide stable magnetic fields. These attempts were abandoned for most applications, however, due to their inability to provide adequate field strength. Subsequent designs utilizing better current regulating circuitry were exclusively electromagnetic. A glance through a typical textbook on scanning electron microscopes will reveal the bulky, complicated, inflexible nature of these prior art systems, which could easily fill a large room.
In view of the current state of scanning electron microscope systems as explained above, there is clearly a need for a smaller sized, less complicated, and more flexible scanning electron microscope system and system components.